This invention relates to a vehicle AC generator control system.
A vehicle AC generator is driven through a V-belt by the engine, to convert rotational energy into electrical energy. There has been a demand for provision of a high power vehicle AC generator for an increasing vehicle electrical load. The increase in output of the vehicle AC generator means the increase in load torque of the engine. Hence, the rotation of the engine is liable to become unstable when the explosion and combustion are unstable for instance immediately after the start of the engine. In addition, at the start of the engine, the generator provides its maximum output to charge the battery which has been discharged to operate the starter motor, and accordingly the load on the engine is increased as much; that is, the rotation of the engine becomes more unstable. This phenomenon occurs significantly when the ambient temperature is low.
In order to overcome this difficulty, a control device has been proposed, for instance, by Published Unexamined Japanese Patent Application (OPI) No. 66538/1983 (the term "OPI" as used herein means an "unexamined published application") in which, when the rotation of the engine is unstable immediately after the start, the amount of current supplied to the field coil is limited for a certain period of time to decrease the engine load, thereby to stabilize the engine idling rotation.
The above-described control device controls the field current for a certain period of time from the start of the engine, as was described above. Therefore, the generator output is suppressed, but it will not become zero (A). Hence, with the device, it is difficult to completely eliminate the generator drive load torque; that is, the rotation of engine cannot be sufficiently stabilized.
In general, when it is cold, the V-belt and pulleys for driving a vehicle generator are not sufficiently engaged with one another. Therefore, in the case of the above-described conventional control device, when the generator produces drive torque, the belt slips thus producing noises (hereinafter referred to as "belt slip noises", when applicable).
Furthermore, with the conventional control device, a certain period of time from the start of the engine the field current is abruptly increased, and accordingly the generator output is also abruptly increased; that is, the engine load is abruptly increased, so that the belt slip noise is liable to be produced. In addition, the abrupt increase of the engine load may adversely affect the rotation of the engine.